A 5-level efficient IFPWM power coding approach encoding LTE for class-S digital-RF transmitter with distortion correction

Abstract

In this work, for the first time we propose a multi-level intermediate frequency pulse width modulation (ML-IFPWM) power coding approach to generate a high speed pulse train as input of GHz class-S switch-mode PA in the digital-RF transmitter. The key feature of a high power coding efficiency of 68.5% from a 5-level digitally implemented discrete-time (DT)-PWM quantizer encoding 20-MHz LTE signal (PAR of 10.25-dB) is verified by simulation. Unlike the traditional RFPWM, this new power coding process taking place at IF frequency of 100 MHz, offers a higher over-sampling ratio thus resulting in an improved output spectrum purity. In addition, a look-up-table based linearization unit is introduced in the digital-RF transmitter architecture to specifically correct the distortion caused by the nonlinear transformation of power encoder. To the author's knowledge, this is the most efficient power coding approach in a digital implementation reported so far encoding 20-MHz LTE at 2 GHz with low EVM of 4.1%.